The present invention relates generally to an in-mold transfer method for simultaneously achieving injection molding and transference of a transfer foil from a transfer film placed in dies onto the surface of an injection-molded product, and more particularly, to a resin wheel cover molded using the method.
An in-mold transfer method for simultaneously achieving injection molding and transference of a transfer layer from a transfer film placed in dies onto the surface of an injection-molded product is known. This in-mold transfer method is carried out in accordance with the following steps.
As shown in FIG. 10A, a transfer film 54 for in-mold transferring is placed in a mold consisting of a first die 51 and a second die 52. The transfer film 54 is composed of a base film 55 and a transfer layer 56. Next, as shown in FIG. 10B, a molten resin is injected from an injection molding machine 57 into the dies 51 and 52. The resin fills the dies 51 and 52 conforming to the configuration of the cavity and core and also presses the transfer film 54. Thus, the transfer layer 56 is separated from the base film 55 and transferred onto the resin 59. The first and second dies 51 and 52 are separated from each other after the resin is cured, as shown in FIG. 10C, to obtain a resin product having the transfer layer 56 transferred thereon.
Meanwhile, wheel covers are resin products that can be produced by this known injection molding method. There are various shapes of wheel covers, and the in-mold transfer method can be used for producing those having substantially flat surfaces. However, some wheel covers have heat dissipation holes for dissipating heat generated by braking. A cross-sectional view of such a wheel cover 61 is shown in FIG. 11. This wheel cover 61 has communicating holes 64, each communicating a front face 62 and a rear face 63, and a decorative face 66 formed on the front face 62 around each communicating hole 64. The communicating hole 64 has a collar 65 extending from the rear face 63. The collar 65 is tapered such that the diameter of the collar 65 is smaller toward its distal end. The collars 65 are formed mainly for giving the impression that the wheel cover 61 is thick, i.e., the wheel cover 61 appears thicker than it actually is, when the collars 65 of the wheel cover 61 are viewed through the communicating holes 64.
The wheel cover 61 is molded by injecting a resin into a first die 68 and a second die 69, as shown in FIG. 12, and, after the resin is cured, the dies 68 and 69 are separated from each other to take the cured resin product out of the dies 68 and 69.
However, it is sometimes difficult to apply the in-mold transfer method to wheel covers like the wheel cover having decorative faces 66 formed around the communicating holes 64. More specifically, the transfer layer 56 is extended on the decorative faces 66 and on the inner wall surface of the communicating hole 64, as shown in FIG. 13. The transfer layer 56 may be broken if the inclination of the decorative faces 66 is steep and the transfer layer 56 is pulled much beyond its critical point of extension, or if it is wrinkled. If the transfer layer 56 is extended too much, even if it is not broken or wrinkled, the transfer layer 56, which is based on an aluminum vapor deposition layer, undergoes whitening and loses its primary metallic luster.
For solving this problem, the parting line (PL face) 70 of the first die 68 and the second die 69 may be shifted toward the front face 62, as shown in FIG. 14. In this case, the transfer layer 56 is merely extended to the Parting line 70, so that the problems attributed to excessive extension are avoided. However, according to this proposal, the tapered collars 65 hinder separation of the first die 68 from the second die 69. if the collars 65 are omitted, the wheel cover 61 does not appear to have greater thickness, and the rigidity around the communicating holes is lowered.